With increasingly fast transmission rate of fiber-optic communication, the communication system becomes more and more sensitive to a series of damage induced by polarization, for example, polarization mode dispersion generated in the process of transmission. These damages are mainly attributable to the defects of optical fiber itself. In the case of idealized optical fiber, the polarization state is maintained unchanged and the damages caused by polarization effect can be readily eliminated. In contrast, in the case of standard communication optical fiber in practical use, the polarization state of transmitted light is constantly changed due to irregular double refraction caused by for example thermal stress, mechanical stress in optical fiber as well as irregularity of fiber core.
To address this problem, polarization controllers are employed to eliminate such damages and they function to transform any designated polarization states to any desirable ones. Today, the polarization controllers available mainly include manual or electric adjustable polarization controls and 3-paddle fiber polarization controller which, however, are all disadvantageous in that they are large in volume and have unsatisfactory performance. For example, the prior-art 3-paddle controllers have an optical fiber fully secured at both ends. This would lead to twisting of the optical fiber at both ends, causing considerable damages to the optical fiber. Moreover, the prior-art controllers generally squeeze an optical fiber before rotating it, which would result in additional twisting of the optical fiber itself. To mitigate the damage to optical fibers resulting from twisting, the common practice is enlarging the volume of polarization controller thereby reducing the relative twisting length.